Leading edge structure for a flow control system of an aircraft

ABSTRACT

A leading edge structure ( 1 ) for a flow control system of an aircraft ( 101 ) including a double-walled leading edge panel ( 3 ) with a first side portion ( 11 ) extending to a first attachment end ( 17 ), a second side portion ( 13 ) extending to a second attachment end ( 19 ), an inner wall element ( 21 ) facing a plenum ( 7 ), an outer wall element ( 23 ) facing ambient flow ( 25 ), and a core assembly ( 97 ). The outer wall element ( 23 ) includes micro pores ( 31 ) and the inner wall element ( 21 ) includes openings ( 33 ) which form a fluid connection from ambient flow, through the core assembly ( 97 ) and to the plenum ( 7 ). The thickness of the outer wall element is reduced due to the first attachment end ( 17 ) and/or at the second attachment end ( 19 ) attached to the inner wall element ( 21 ) by both bonding and fasteners ( 85, 87, 89, 91 ).

RELATED APPLICATIONS

This application incorporates by reference and claims priority to GermanPatent Application DE 10 2021 101 444.1 filed Jan. 22, 2021, and GermanPatent Application DE 10 2021 116 932.1 filed Jun. 30, 2021.

BACKGROUND

The present invention relates to a leading edge structure for a flowcontrol system of an aircraft, in particular for a Hybrid Laminar FlowControl (HLFC) system, where air is sucked in or blown out of a poroussurface of a flow body in order to extend the region of laminar flowalong the flow body. Further aspects of the present invention relate toa vertical tail plane comprising such a leading edge structure, and anaircraft comprising such a leading edge structure or such a verticaltail plane. Instead of to a vertical tail plane the leading edgestructure might also be attached to a horizontal tail plane or to awing.

The leading edge structure comprises a double-walled leading edge panelthat surrounds a common plenum in a curved, i.e. arcuate, manner. Theplenum extends in a span direction through the leading edge structure.

When viewed in a cross section across the span direction, the leadingedge panel has a first side portion extending from a leading edge point,i.e. from a fore tip of the leading edge structure, to a firstattachment end on a first side of the leading edge structure, the firstattachment end being configured for attachment to a further structurelocated downstream from the leading edge, such as a vertical tail planebox. Further, the leading edge panel has a second side portion oppositethe first side portion, wherein the second side portion extends from theleading edge point to a second attachment end on a second side of theleading edge structure opposite the first side, the second attachmentend being configured for attachment to a further structure downstreamfrom the leading edge, such as a vertical tail plane box.

The leading edge panel comprises an inner wall element facing the plenumand spaced apart from the inner wall an outer wall element for contactwith the ambient flow. Between the inner and outer wall elements theleading edge panel comprises a core assembly. The outer wall elementcomprises a plurality of micro pores, such as perforations, forming afluid connection between the core assembly and the ambient flow. Theinner wall element comprises openings forming a fluid connection betweenthe core assembly and the plenum. The inner wall element may be made offiber reinforced plastic (FRP) and the outer wall element may be made oftitanium sheet.

Similar leading edge structures are known in the art. In some knownleading edge structures the outer wall element is attached to the innerwall element in the area of the first and second attachment ends byfasters. In order for the outer wall element to be perforated with micropores it is advantageous to have an outer wall element with a minimumthickness. However, the thickness of the outer wall element is limitedby its post-buckling behavior. The smaller the thickness of the outerwall element the more it tends to buckle, in particular at the first andsecond attachment ends, where the outer wall element is attached to theinner wall element by fasteners. This buckling introduces high pull-outforces into the fasteners, which in turn limits the minimum thickness ofthe outer wall element.

SUMMARY OF INVENTION

Therefore, the present invention may be embodied to provide a leadingedge structure that allows for a minimized thickness of the outer wallelement. The leading edge structure may have a first attachment endand/or at the second attachment end of an outer wall element thatattaches, e.g., directly, to an inner wall element by both bondingand/or fasteners, such as rivets, bolts, or lockbolts. The bondinginhibits buckling of the outer wall element at the first and secondattachment ends, thereby decreasing the pull out loads of the fasteners,which in turn allows to minimize the thickness of the outer wallelement. A minimum thickness of the outer wall element saves weight andsimplifies introduction of the micro pores into the outer wall element.

The first attachment end and/or at the second attachment end the outerwall element may rest against the inner wall element along a commoncontact plane, e.g., in an overlapping, planar or layered manner. Bysuch an areal connection a reliable attachment by bonding and fastenersis enabled.

At the first attachment end and/or at the second attachment end betweenthe outer wall element and the inner wall element a bonding layer may beprovided extending within the contact plane, e.g., only a bonding layerand no other structure. The bonding layer might be of various form andmaterial and provides a reliable areal connection.

The bonding layer may be made of a film adhesive. This bonding materialprovides reliable adhesion between the FRP and titanium material of theinner and outer wall elements.

The bonding layer may have a thickness of between 0.1 millimeter (mm)and 0.2 mm, e.g., 0.1 mm. Such a thickness of the bonding layer providesadhesion for the inner and outer wall elements.

The bonding layer may have a peeling strength of at least 150 N/mm(newtons per mm), e.g., between 200 N/mm and 250 N/mm. The peelingstrength is measured by coupon test. In such a way, pull out loads ofthe fasteners can be reliably reduced.

At the first attachment end and/or at the second attachment end aplurality of fasteners may extend through both the outer wall elementand the inner wall element, as they are resting against one another, aswell as through the bonding layer in between the inner and outer wallelements. The fasteners may be arranged in one or more lines offasteners extending in the span direction. The fasteners together withthe bonding layer provide a reliable hybrid connection between the firstand second wall elements.

The outer wall element may extend from the first attachment end to thesecond attachment end. In this way, a leading edge structure with aone-step, continuous and smooth flow surface is provided that does notform an obstacle for ambient flow streaming along the flow surface and,thus, decreases drag and increases flow efficiency of the leading edgestructure. Further, the area of the micro pores can be extended furtherdownstream closer to the attachment ends, thereby increasing the overallflow control effectivity. Moreover, the leading edge structure can beoptimized in terms of weight and costs since the outer wall element alsosupports the attachment ends.

The core assembly may comprises a plurality of elongate stiffenersconnecting the inner and outer wall elements and spaced apart from oneanother, so that between each pair of adjacent stiffeners a hollowchamber is formed between the inner and outer wall elements. Thestiffeners may be formed from FRP integrally with the inner wallelement. The plurality of micro pores form a fluid connection betweenthe hollow chambers and the ambient flow, while the openings form afluid connection between the hollow chambers and the plenum. Each hollowchamber may comprise at least one opening. Such stiffeners and hollowchambers form a simple and effective core assembly through which airflow can pass during suction or blowing operation.

The outer wall element may form a first end edge at the first attachmentend and a second end edge at the second attachment end. The first endedge and/or second end edge may extend in parallel to the leading edgeand may be formed to extend along or rest against a vertical tail planebox of a related vertical tail plane. This means, the outer wall elementextends as far as or even further downstream as the inner wall elementat the first attachment end and/or at the second attachment end. In sucha way, a full outer coverage of the leading edge structure by outer wallelement is achieved.

The first end edge and/or the second end edge may extend in parallel toat least one of and possibly all of the stiffeners. This means, the endedges extend in span direction. In such a way, the end edges cancontinuously abut a vertical tail plane box when the leading edgestructure is attached to a vertical tail plane.

The outer wall element may comprises a main wall portion as well as afirst wall extension and/or a second wall extension. The main wallportion includes the leading edge point. The first wall extensionincludes the first attachment end and may include the first end edge.The second wall extension includes the second attachment end and mayinclude the second end edge. In such a way, the outer wall element mightbe formed by connecting the first and second wall extensions to the mainwall portion, so that for the main wall portion a titanium sheet mightbe used with a width as available on the marked, while the remainingwidth required to cover the full leading edge panel from the firstattachment end to the second attachment end can be covered by the firstand second wall extensions.

The first wall extension may be connected to the main wall portion suchvia a straight first welding seam. Alternatively or additionally, thesecond wall extension is connected to the main wall portion via awelding seam, e.g., a straight second welding seam. First and/or secondwelding seams may be butt-welded seams, e.g., formed by laser welding.Other forms of welding or alternative forms of connection of the mainwall portion to the first and/or second wall extensions are alsopossible.

The first welding seam and/or the second welding seam may be dressed, atleast at the outer flow surface in contact with the ambient flow, toform a smooth transition between the main wall portion and the firstwall extension and/or between the main wall portion and the second wallextension. In such a way, the first and second welding seams do not forma flow obstacle and laminar flow across the welding seams is possible.

The first welding seam, e.g., the entire first wall extension, may beattached, e.g., bonded, directly and planar to the inner wall elementwith no core assembly in between. Additionally or alternatively, thesecond welding seam, e.g., the entire second wall extension, isattached, e.g., bonded, directly and planar to the inner wall elementwith no core assembly in between. In such a way, the first and secondwelding seams are sufficiently supported by the inner wall element,wherein the bonding may form an additional load path. No micro pores maybe present in the first and/or second wall extensions.

The micro pores may be present in the main wall portion, e.g., only inthe main wall portion, and are distributed from the leading edge pointto the first welding seam and/or to the second welding seam, e.g., witha minimum distance from the welding seams. In such a way, the entiremain wall portion can be used for flow control, thereby increasingoverall flow control efficiency of the leading edge structure. A minimumdistance of the micro pores from the first and/or second welding seammay be kept to avoid welding influence on the micro pores.

The stiffeners, in particular at least some of the stiffeners, areformed integrally with the inner wall element. Integrally in thisconnection is to be understood as formed in one piece that is notseparable or mounted together from separate components. Such a leadingedge structure with stiffeners formed integrally with the inner wallelement represents a very simple and light weight construction, sincefasteners, such as bolts or rivets, can be avoided. Also, the mechanicalproperties are improved, so that material and, once again, weight can besaved. Additionally, manufacturing can be simplified and expedited, asthe inner wall element can be formed together with the stiffeners in onecommon process step, e.g. by Resin Transfer Molding (RTM).

The leading edge structure further may comprise a back wall, inparticular a membrane of CFRP material. The back wall may connect thefirst attachment end to the second attachment end of the leading edgepanel, thereby enclosing the plenum together with the leading edge panelon a side opposite the leading edge point.

The openings may be formed as throttle holes having a predefineddiameter adapted for a predefined mass flow rate through the throttleholes in order to achieve a predefined fluid pressure in the hollowchambers. In such a way, the mass flow rate through the micro pores canbe controlled by the fluid pressure in the hollow chambers and, thus, bythe predefined diameter of the throttle holes. Alternatively, theopenings might also be formed such that they allow an uncontrolled massflow rate and are not adapted to control the fluid pressure in thehollow chambers, for example by a number of bores or by one largediameter hole. In this case, the fluid pressure in the hollow chamberscorresponds to the fluid pressure in the plenum, so that the mass flowrate through the micro pores can be controlled only by the fluidpressure in the plenum. Whether the openings are formed as throttle holeor as simple openings not adapted for a specific mass flow rate, mayvary from chamber to chamber.

The stiffeners may have a solid cross section with a square or trapezoidshape. In such a way, the stiffeners provide plane support surfaced forthe inner and outer walls elements.

The stiffeners may extend in the span direction, e.g. in parallel to theleading edge point, and e.g., in parallel to one another. In such a way,the stiffeners may have a long extension.

The inner wall element may be formed of a Fiber Reinforced Plastic (FRP)material, e.g., from a Carbon Fiber Reinforced Plastic (CFRP) material.Further, the stiffeners might be formed as sandwich structures, eachsandwich structure comprising a core element enveloped on opposite sidesby separate layers of FRP of the inner wall element. In other words, theinner wall element splits up in two separate layers. One layer enclosesthe core element on the side facing the plenum, and thus forms the innerwall element in the region of the stiffeners. The other layer enclosesthe core element on the side facing the outer wall element or restingagainst the outer wall element. This layer may be formed in an omegashape, i.e. has an omega-shaped cross section. In such a way, a simple,strong and light weight integral construction of the inner wall elementand the stiffeners is provided.

The core elements may be formed of a foam material. Foam has a highstiffness at a low weight.

A plurality of support ribs, i.e. frames, may be attached to the innerwall element in such a way that they face the plenum and extend across,e.g., perpendicular to, the span direction along the inner wall element.The support ribs stiffen the leading edge structure across the spandirection.

The support ribs may be formed integrally with the inner wall element.In such a way, the inner wall element can be formed as one piecetogether with both the stiffeners and the support ribs. This furthersimplifies the entire leading edge structure and reduces additionalweight.

The support ribs may be formed of FRP. This allows that the support ribscan easily be formed integrally with the inner wall element.

The outer wall element may formed as a titanium sheet. Such titaniumsheet provides the strength and stiffness required for the outer surfacealong the leading edge.

The outer wall element may comprise multiple sections, when viewed froma leading edge downstream, i.e. in a chord direction. The porosityvaries from one section to another in terms of pore diameter and/or porepitch. In particular, the diameter decreases and the pitch increasingfrom the leading edge downstream. In such a way, the mass flow rate ofthe air sucked in or blown out can be adapted to the demand. Forexample, in sections close to the leading edge point, where a highermass flow rate is demanded, the pore diameter might be larger and/or thepore pitch might be smaller than in sections further downstream.

A further aspect of the present invention may be embodied in a verticaltail plane for an aircraft. The vertical tail plane comprises a verticaltail plane box and a leading edge structure according to any of theafore-described embodiments. The vertical tail plane box has a firstlateral panel with a first attachment portion and an opposite secondlateral panel with a second attachment portion. Both the firstattachment portion and the second attachment portion extend in the spandirection. The first attachment end is attached to the first attachmentportion, such that the first end edge extends along, may rest against,the first attachment portion, and the second attachment end is attachedto the second attachment portion, such that the second end edge extendsalong, may rest against, the second attachment portion, so that thefirst side portion of the leading edge panel forms a continuous, e.g.,smooth, flow surface with the first lateral panel of the vertical tailplane box, and the second side portion of the leading edge panel forms acontinuous, e.g. smooth, flow surface with the second lateral panel ofthe vertical tail plane box. The plenum may be in fluid connection withan air outlet, such as an adjustable outlet flap with a rear-facingopening, for causing a vacuum in the plenum to draw ambient air throughthe micro pores and the hollow chambers into the plenum. Further theplenum may be in fluid connection with an air inlet, such as anadjustable inlet flap with a forward-facing opening, for causing anoverpressure in the plenum to blow out air from the plenum through thehollow chambers and the micro pores to the ambient. The air outlet andthe air inlet may be provided in a cover panel on one side or onopposite sides of the vertical tail plane. The vertical tail plane mayfurther comprise a connection duct connecting a lower end of the plenumto the air outlet and/or to the air inlet. The above explanations withrespect to the leading edge structure apply vis-à-vis to the verticaltail plane.

The first attachment end may be attached to the first attachment portionby a first front line of fasteners extending through the main wallportion, and by a first rear line of fasteners extending through thefirst wall extension, so that the first welding seam extends between thefirst front line of fasteners and the first rear line of fasteners.Additionally or alternatively, the second attachment end is attached tothe second attachment portion by a second front line of fastenersextending through the main wall portion, and by a second rear line offasteners extending through the second wall extension, so that thesecond welding seam extends between the second front line of fastenersand the second rear line of fasteners. The fasteners can be e.g. bolts,lockbolts and rivets. In such a way, the main wall portion and the firstand second wall extensions are each secured to the first attachmentportion and the second attachment portion, respectively, by at least oneline of fasteners, so that the first welding seam and the second weldingseam, respectively, are not necessarily required for structuralintegrity of the outer wall element.

The first front line of fasteners and/or the second front line offasteners may extend through a back wall connecting the first attachmentend to the second attachment end of the leading edge panel, to attachthe back wall to the leading edge panel. A flange of the back wall mayrest against an inner surface of the inner wall element in anoverlapping manner. Additionally or alternatively, the first rear lineof fasteners extend through the first attachment portion of the verticaltail plane box to attach the vertical tail plane box to the leading edgepanel. The first attachment portion may rest against the inner surfaceof the inner wall element in an overlapping manner. Additionally oralternatively, the second rear line of fasteners extend through thesecond attachment portion of the vertical tail plane box to attach thevertical tail plane box to the leading edge panel. The second attachmentportion may rest against the inner surface of the inner wall element inan overlapping manner. In such a way, the back wall and/or the verticaltail plane box can be attached to the leading edge panel by the samefasteners used to attach the inner and outer wall element to oneanother.

Yet a further aspect of the present invention may relate to an aircraftcomprising a leading edge structure according to any of theafore-described embodiments, or comprising a vertical tail planeaccording to any of the afore-described embodiments. The aboveexplanations with respect to the leading edge structure and the verticaltail plane apply vis-à-vis to the aircraft.

Yet a further aspect of the present invention may relate to a method formanufacturing a leading edge structure according to any of theafore-described embodiments comprising the following steps: The innerwall element and the core assembly is produced, wherein the stiffenersand the inner wall element are formed together as an integral part by aResin Transfer Molding (RTM) process, in particular by a common RTMstep. The support ribs may be formed as an integral part together withthe inner wall element and the stiffeners by an RTM process. Further,the outer wall element is produced. Then, the outer wall element isconnected, e.g., bonded, to the core assembly and/or to the inner wallelement, wherein the outer wall element may be bonded against thestiffeners and against the inner wall element at the first and/or secondattachment ends. At the first and second attachment ends, the inner andouter wall elements are additionally attached to one another byfasteners, such as rivets bolts, or lockbolts. The above explanationswith respect to the leading edge structure also apply to the presentmethod.

The outer wall element may be produced using the following steps: Themain wall portion is provided, such as formed by a titanium sheet of1.25 meter (m) width and 1 mm thickness. The first wall extension and/orthe second wall extension are provided, e.g. titanium sheets of 0.125 mwidth each and 1 mm thickness. Then, the main wall portion is welded,e.g., butt-welded, to the first wall extension to form the first weldingseam, and/or to the second wall extension to form the second weldingseam, e.g., by laser welding. By butt-welding the main wall portion tothe first and/or second wall extensions a reliable and smooth connectionbetween these parts can be produced.

The first welding seam and/or the second welding seam may subsequentlybe dressed, at least at the outer flow surface in contact with theambient flow, to form a smooth transition between the main wall portionand the first wall extension and/or between the main wall portion andthe second wall extension. In such a way, the welding seams do not forman obstacle to the ambient flow thereby allowing a laminar flow alongthe flow surface.

The following steps may be carried out to produce the outer wallelement: First, a blank of the main wall portion is provided. Then, themicro pores are produced in the blank after which it is sanded andetched. Subsequently, the first and/or second wall extensions areprovided and welded to the main wall portion to form the first and/orsecond welding seams. After welding the first and/or welding seams aredressed to form a smooth and continuous surface. Finally, the outer wallelement is formed, in particular bent, to the final curved shape of theleading edge.

SUMMARY OF DRAWINGS

Embodiments of the invention are illustrated in the drawings which are:

FIG. 1 is a perspective view of an aircraft,

FIG. 2 is a perspective cut open view of an embodiment of a leading edgestructure according to an embodiment of the invention,

FIG. 3 is a cross sectional view across the span direction of theleading edge structure shown in FIG. 2,

FIG. 4 is a detailed view of the second attachment end of the leadingedge structure shown in FIG. 3,

FIG. 5 is a detailed view of a hollow chamber of the leading edgestructure shown in FIG. 3,

FIG. 6 is a detailed view of another hollow chamber of the leading edgestructure shown in FIG. 3, wherein the inner wall element has an openingformed as a throttle hole,

FIG. 7 is an exploded view of the leading edge structure shown in FIG.3,

FIG. 8 is a perspective view of the outer wall element of the leadingedge structure shown in FIG. 7, indicating the first and second weldingseams,

FIG. 9 is a side view of a vertical tail plane for an aircraftcomprising the leading edge structure shown in FIG. 2,

FIG. 10 is a detailed perspective view of a connection duct of thevertical tail plane shown in FIG. 9, and

FIG. 11 is another perspective view of the connection duct shown in FIG.10.

DETAILED DESCRIPTION

In FIG. 1 an aircraft 101 according to an embodiment of the presentinvention is shown. The aircraft comprises a fuselage 103, wings 105, ahorizontal tail plane 107, and a vertical tail plane 109 according to anembodiment of the invention. The vertical tail plane 109 is shown inmore detail in FIG. 9. The vertical tail plane 109 comprises a leadingedge structure 1 according to an embodiment of the invention. Variousembodiments of the leading edge structure 1 are shown in more detail inFIGS. 2 to 8.

In FIGS. 2 and 3 an embodiment of a leading edge structure 1 for a flowcontrol system of an aircraft according to the present invention isshown. The leading edge structure 1 comprises a double-walled leadingedge panel 3 and a back wall 5.

The leading edge panel 1 surrounds a plenum 7 in a curved manner,wherein the plenum 7 extends in a span direction 9. The leading edgepanel 3 has a first side portion 11 and an opposite second side portion13. The first side portion 11 extends from a leading edge point 15 to afirst attachment end 17. The second side portion 13 extends from theleading edge point 15 to a second attachment end 19, as shown in FIG. 4.

The back wall 5 is formed as a membrane of CFRP material and connectsthe first attachment end 17 to the second attachment end 19 of theleading edge panel 3. In such a way, the back wall 5 encloses the plenum7 together with the leading edge panel 3 on a side opposite the leadingedge point 15.

The leading edge panel 3 comprises an inner wall element 21 facing theplenum 7 and an outer wall element 23 in contact with an ambient flow25. Between the inner and outer wall elements 21, 23 the leading edgepanel 3 comprises a core assembly 97 comprising a plurality of elongatestiffeners 27 spaced apart from one another, so that between each pairof adjacent stiffeners 27 a hollow chamber 29 is left open between theinner and outer wall elements 21, 23, as shown in FIG. 5. The stiffeners27 extend in the span direction 9 in parallel to the leading edge point15 and in parallel to one another.

The outer wall element 23 comprises a plurality of micro pores 31forming a fluid connection between the hollow chambers 29 and theambient flow 25. The inner wall element 21 comprises openings 33 forminga fluid connection between the hollow chambers 29 and the plenum 7. Atsome of the hollow chambers 29, the openings 33 are formed as throttleholes 35 having a predefined diameter 37 adapted for a predefined massflow rate through the throttle holes 35 in order to achieve a predefinedfluid pressure in the hollow chambers 29, as it is shown in FIG. 6.However, at others of the hollow chambers 29, the openings 33 are formedto allow a random mass flow rate and are not adapted to control thefluid pressure in the hollow chambers 29, as it is the case in thehollow chamber 29 shown in FIG. 5.

The stiffeners 27 are formed integrally with the inner wall element 21.The inner wall element 21 is formed of a Carbon Fiber Reinforced Plastic(CFRP). The stiffeners 27 have a solid trapezoid-shaped cross sectionand are formed as sandwich structures 39. Each sandwich structure 39comprises a core element 41 enveloped on opposite sides by first andsecond separate layers 43 a, 43 b of CFRP of the inner wall element 21,wherein one layer 43 a encloses the core element 41 on the side facingthe plenum 7, while the other layer 43 b encloses the trapezoid surfaceof the core element 41 on the side facing the outer wall element 23 byan omega-shape curse. The core elements 41 are formed of a foammaterial.

As shown in FIG. 2, a plurality of support ribs 45 are attached to theinner wall element 21 in such a way that they face the plenum 7 andextend perpendicular to the stiffeners 27 and to the span direction 9along the inner wall element 21. The support ribs 45 are formedintegrally with the inner wall element 21 and are also formed of a CFRPmaterial.

The outer wall element 23 is formed as a titanium sheet and comprisesmultiple sections 47 a, 47 b, 47 c arranged subsequently in a chorddirection 49. The porosity varies from one section 47 a to anothersection 47 b, 47 c in terms of the pore pitch, wherein the pore pitchincreases from the leading edge point 15 downstream.

As shown in FIGS. 4, 7 and 8, the outer wall element 23 extends from thefirst attachment end 17 to the second attachment end 19. The outer wallelement 23 forms a first end edge 51 at the first attachment end 17 anda second end edge 53 at the second attachment end 19. The first end edge51 and the second end edge 53 extend in parallel to the leading edge 54and are formed to extend along or rest against a vertical tail plane box55 of the associated vertical tail plane 109. This means, the outer wallelement 23 extends as far as the inner wall element 21 at the firstattachment end 17 and at the second attachment end 19. The first endedge 51 and the second end edge extend 53 in parallel to the stiffeners27. This means, the end edges 51, 53 extend in span direction 9.

The outer wall element 23 comprises a main wall portion 59 as well as afirst wall extension 61 and a second wall extension 63. The main wallportion 59 includes the leading edge point 15. The first wall extension61 includes the first attachment end 17 and the first end edge 51. Thesecond wall extension 63 includes the second attachment end 19 and thesecond end edge 53. As shown in FIGS. 7 and 8, the first wall extension61 is connected to the main wall portion 59 via a straight first weldingseam 67. Additionally, the second wall extension 63 is connected to themain wall portion 59 via a straight second welding seam 69. First andsecond welding seams 67, 69 are butt-welding seams formed by laserwelding. The first welding seam 67 and the second welding seam 69 aredressed at the outer flow surface 71 to form a smooth transition betweenthe main wall portion 59 and the first wall extension 61 and between themain wall portion 59 and the second wall extension 63.

As shown in FIG. 4, the first welding seam 67 and the entire first wallextension 61 are bonded directly and planar to the inner wall element 21with no core assembly 97 in between. Additionally, the second weldingseam 69 and the entire second wall extension 63 are bonded directly andplanar to the inner wall element 21 with no core assembly 97 in between.A bonding layer 98 extends directly between the inner and outer wallelements 21, 23 within a contact plane 99 at the first and secondattachment ends 17, 19. No micro pores 31 are present in the first andsecond wall extensions 61, 63. As indicated in FIG. 7, the micro pores31 are present only in the main wall portion 59 and are distributed fromthe leading edge point 15 to the first welding seam 67 and to the secondwelding seam 69 with a minimum distance from the welding seams 67, 69.

As also shown in FIG. 4, at the first attachment end 17 and at thesecond attachment end 19 the outer wall element 23 is additionallyattached to the inner wall element 21 by fasteners 85, 87, 89, 91, i.e.bolts, rivets or lockbolts, so that at the first and second attachmentends 17, 19 the outer wall element 23 is attached to the inner wallelement 21 by both bonding layer 98 and fasteners 85, 87, 89, 91. At thefirst attachment end 17 and at the second attachment end 19 the outerwall element 23 rests against the inner wall element 21 along the commoncontact plane 99 in an overlapping and planar manner, wherein within thecontact plane 99 the bonding layer 98 is provided. The bonding layer 98is made of film adhesive, has a thickness of between 0.1 and 0.2 mm, andhas a peeling strength in the range above 150 N/mm.

FIGS. 9 to 11 show a vertical tail plane 109 for an aircraft 101according to the invention. The vertical tail plane 109 comprises avertical tail plane box 55 and a leading edge structure 1 as describedbefore. The vertical tail plane box 55 has a first lateral panel 75 witha first attachment portion 77 and an opposite second lateral panel 79with a second attachment portion 81. The first attachment end 17 of theleading edge panel 3 is attached to the first attachment portion 77 suchthat the first end edge 51 extends along the first attachment portion77, and the second attachment end 19 of the leading edge panel 3 isattached to the second attachment portion 81 such that the second endedge 53 extends along the second attachment portion 81. The first sideportion 11 of the leading edge panel 3 forms a continuous flow surface71 with the first lateral panel 75 of the vertical tail plane box 55,and the second side portion 13 of the leading edge panel 3 forms acontinuous flow surface with the second lateral panel 79 of the verticaltail plane box 55. The plenum 7 is in fluid connection with an airoutlet 83 for causing a vacuum in the plenum 7 to draw air from theambient flow 25 through the micro pores 31 and the hollow chambers 29into the plenum 7.

As shown in FIGS. 4 and 8, the first attachment end 17 is attached tothe first attachment portion 77 by a first front line of fasteners 85extending through the main wall portion 59, and by a first rear line offasteners 87 extending through the first wall extension 61, so that thefirst welding seam 67 extends between the first front line of fasteners85 and the first rear line of fasteners 87. Additionally, the secondattachment end 19 is attached to the second attachment portion 81 by asecond front line of fasteners 89 extending through the main wallportion 59, and by a second rear line of fasteners 91 extending throughthe second wall extension 63, so that the second welding seam 69 extendsbetween the second front line of fasteners 89 and the second rear lineof fasteners 91. The fasteners 85, 87, 89, 91 can be e.g. bolts,lockbolts, rivets.

The first front line of fasteners and/or the second front line offasteners may extend through a back wall connecting the first attachmentend to the second attachment end of the leading edge panel, to attachthe back wall to the leading edge panel. A flange of the back wall mayrest against an inner surface of the inner wall element in anoverlapping manner. Additionally or alternatively, the first rear lineof fasteners extend through the first attachment portion of the verticaltail plane box to attach the vertical tail plane box to the leading edgepanel. The first attachment portion may rest against the inner surfaceof the inner wall element in an overlapping manner. Additionally oralternatively, the second rear line of fasteners extend through thesecond attachment portion of the vertical tail plane box to attach thevertical tail plane box to the leading edge panel. The second attachmentportion may rest against the inner surface of the inner wall element inan overlapping manner. In such a way, the back wall and/or the verticaltail plane box can be attached to the leading edge panel by the samefasteners used to attach the inner and outer wall element to oneanother.

As shown in FIG. 4, the first front line of fasteners 85 and the secondfront line of fasteners 89 extend through the back wall 5 connecting thefirst attachment end 17 to the second attachment end 19 of the leadingedge panel 3, to attach the back wall 5 to the leading edge panel 3. Aflange 100 of the back wall 5 rests against an inner surface of theinner wall element 21 in an overlapping manner. Additionally, the firstrear line of fasteners 87 extend through the first attachment portion 77of the vertical tail plane box 55 to attach the vertical tail plane box55 to the leading edge panel 3. The first attachment portion 77 restsagainst the inner surface of the inner wall element 21 in an overlappingmanner. Additionally, the second rear line of fasteners 91 extendthrough the second attachment portion 81 of the vertical tail plane box55 to attach the vertical tail plane box 55 to the leading edge panel 3.The second attachment portion 81 rests against the inner surface of theinner wall element 21 in an overlapping manner.

As shown in FIGS. 10 and 11, the vertical tail plane 109 furthercomprises a connection duct 93 connecting a lower end 95 of the plenum 7to the air outlet 83. In addition to the air outlet flap 83 the plenum 7might also be in fluid connection with an air inlet (not shown) forcausing an overpressure in the plenum 7 to blow out air from the plenum7 through the hollow chambers 29 and the micro pores 31 to the ambientflow 25.

The leading edge structure 1 shown in FIGS. 2 to 8 can be manufacturedby a method including the following steps: The inner wall element 21 andthe core assembly 97 is produced, wherein the stiffeners 27 and theinner wall element 21 are formed together as an integral part by a ResinTransfer Molding (RTM) process in a common RTM step. Also the supportribs 45 are formed as an integral part together with the inner wallelement 21 and the stiffeners 27 by an RTM process. Further, the outerwall element 23 is produced. Then, the outer wall element 23 is bondedto the core assembly 97 and to the inner wall element 21, wherein theouter wall element 23 is bonded against the stiffeners 27 and againstthe inner wall element 21 at the first and second attachment ends 17,19.

The outer wall element 23 is produced comprising the following steps:The main wall portion 59 is provided, which is formed by a titaniumsheet of 1.25 m width and 1 mm thickness. The first wall extension 61and the second wall extension 63 are provided in the form of titaniumsheets of 0.125 m width each and 1 mm thickness. Then, the main wallportion 59 is butt-welded to the first wall extension 61 to form thefirst welding seam 67, and to the second wall extension 63 to form thesecond welding seam 69, by laser welding. The first welding seam 67 andthe second welding seam 69 are subsequently dressed at the outer flowsurface 71 to form a smooth transition between the main wall portion 59and the first wall extension 61 and between the main wall portion 59 andthe second wall extension 63.

By the leading edge structure 1 according to the present invention asdescribed above, the bonding layer 98 inhibits a buckling of the outerwall element 23 at the first and second attachment ends 17, 19, therebyessentially decreasing the pull out loads of the fasteners 85, 87, 89,91, which in turn allows to minimize the thickness of the outer wallelement 23. A minimum thickness of the outer wall element 23 savesweight and simplifies introduction of the micro pores 31 into the outerwall element 23.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

The invention is:
 1. A leading edge structure for a flow control systemof an aircraft comprising: a double-walled leading edge panel thatsurrounds the a plenum in a curved manner, the plenum extending in aspan direction of the leading edge structure; wherein the double-walledleading edge panel has a first side portion extending from a leadingedge point to a first attachment end, wherein the double-walled leadingedge panel has a second side portion opposite the first side portion,extending from the leading edge point to a second attachment end,wherein the double-walled leading edge panel comprises an inner wallelement facing the plenum and an outer wall element for contact with anambient flow, wherein between the inner and outer wall elements thedouble-walled leading edge panel comprises a core assembly, wherein theouter wall element comprises a plurality of micro pores forming a fluidconnection between the core assembly and the ambient flow, and whereinthe inner wall element comprises openings forming a fluid connectionbetween the core assembly and the plenum, and wherein at the firstattachment end and/or at the second attachment end the outer wallelement is attached to the inner wall element by both bonding andfasteners.
 2. The leading edge structure according to claim 1, whereinat the first attachment end and/or at the second attachment end theouter wall element rests against the inner wall element along a commoncontact plane.
 3. The leading edge structure according to claim 2,wherein at the first attachment end and/or at the second attachment endbetween the outer wall element and the inner wall element a bondinglayer is provided extending within the contact plane.
 4. The leadingedge structure according to claim 3, wherein the bonding layer is madeof film adhesive.
 5. The leading edge structure according to claim 3,wherein the bonding layer has a thickness in a range of 0.1 mm to 0.2mm.
 6. The leading edge structure according to claim 3, wherein thebonding layer has a peeling strength of at least 150 N/mm.
 7. Theleading edge structure according to claim 1, wherein at the firstattachment end and/or at the second attachment end a plurality offasteners extend through both the outer wall element and the inner wallelement.
 8. The leading edge structure according to claim 1, wherein theouter wall element extends from the first attachment end to the secondattachment end.
 9. The leading edge structure according to claim 1,wherein the core assembly comprises a plurality of elongate stiffenersspaced apart from one another, so that between each pair of adjacentstiffeners a hollow chamber is formed between the inner and outer wallelements, wherein the plurality of micro pores form a fluid connectionbetween the hollow chambers and the ambient flow, and wherein theopenings form a fluid connection between the hollow chambers and theplenum.
 10. The leading edge structure according to claim 1, wherein theouter wall element forms a first end edge at the first attachment endand a second end edge at the second attachment end.
 11. The leading edgestructure according to claim 10, wherein the first end edge and/or thesecond end edge are parallel to at least one of the stiffeners.
 12. Theleading edge structure according to claim 1, wherein the outer wallelement comprises a main wall portion and a first wall extension and/ora second wall extension, wherein the main wall portion includes theleading edge point, wherein the first wall extension includes the firstattachment end, and wherein the second wall extension includes thesecond attachment end.
 13. The leading edge structure according to claim12, wherein the first wall extension is connected to the main wallportion via a first welding seam, and/or wherein the second wallextension is connected to the main wall portion via a second weldingseam.
 14. The leading edge structure according to claim 13, wherein thefirst welding seam and/or the second welding seam are dressed to form asmooth transition between the main wall portion and the first wallextension and/or between the main wall portion and the second wallextension.
 15. The leading edge structure according to claim 13, whereinthe first welding seam is attached directly to the inner wall element,and/or wherein the second welding seam is attached directly to the innerwall element.
 16. The leading edge structure according to claim 13,wherein the micro pores are present in the main wall portion and aredistributed from the leading edge point to the first welding seam and/orto the second welding seam.
 17. A vertical tail plane configured for anaircraft comprising a vertical tail plane box including a first lateralpanel with a first attachment portion and an opposite second lateralpanel with a second attachment portion, a leading edge structureincluding: a plenum extending in a span direction of the vertical tailplane; a double-walled leading edge panel at least partially surroundingthe plenum, wherein the double-walled leading edge panel includes: aninner wall element facing the plenum; an outer wall element configure tobe in contact with an ambient flow over the vertical tail plane, and acore assembly between the inner wall element and the outer wall element;micro-pores in the outer wall element and openings in the inner wallelement, wherein air from the ambient flow flows through themicro-pores, the core assembly, the openings and into the plenum; afirst side portion of the double-walled leading edge extends from aleading edge point to a first attachment end; and a second side portionof the double-walled leading edge is opposite the first side portion,and extends from the leading edge point to a second attachment end,wherein at the first attachment end and/or at the second attachment endattaches to the inner wall element by both bonding and fasteners;wherein the first attachment end is attached to the first attachmentportion, and the second attachment end is attached to the secondattachment portion, wherein the first side portion of the leading edgepanel forms a continuous flow surface with the first lateral panel ofthe vertical tail plane box, and the second side portion of the leadingedge panel forms a continuous flow surface with the second lateral panelof the vertical tail plane box.
 18. The vertical tail plane according toclaim 17, wherein the first attachment end is attached to the firstattachment portion by a first front line of fasteners extending throughthe main wall portion, and by a first rear line of fasteners extendingthrough the first wall extension, so that the first welding seam extendsbetween the first front line of fasteners and the first rear line offasteners, and/or wherein the second attachment end is attached to thesecond attachment portion by a second front line of fasteners extendingthrough the main wall portion, and by a second rear line of fastenersextending through the second wall extension, so that the second weldingseam extends between the second front line of fasteners and the secondrear line of fasteners.
 19. The vertical tail plane according to claim18, wherein the first front line of fasteners and/or the second frontline of fasteners extend through a back wall connecting the firstattachment end to the second attachment end of the leading edge panel,to attach the back wall to the leading edge panel, and/or wherein thefirst rear line of fasteners extend through the first attachment portionof the vertical tail plane box to attach the vertical tail plane box tothe leading edge panel and/or the second rear line of fasteners extendthrough the second attachment portion of the vertical tail plane box toattach the vertical tail plane box to the leading edge panel.
 20. Anaircraft comprising a leading edge structure according to claim 1.